Semiconductor devices include transistors. A transistor may modulate a current flowing through it in response to an input signal. One example of a type of a transistor is a field effect transistor (FET). An FET may change the characteristics of a channel in response to the input signal. The input signal affects the characteristics of the channel such as the carrier concentration and the carrier type. By affecting the characteristics of the channel, the input signal may modulate current flowing through the channel, and hence, flowing through the transistor. Typically, such a transistor may include a source and a drain coupled to the channel. A gate receives the input signal to modulate the channel.
An FET may also be characterized as an enhancement mode or a depletion mode FET. Enhancement or depletion mode describes the carrier concentrations with no input signal applied. An enhancement mode or a depletion mode FET may also be referred to as a normally off or normally on FET. In a normally on FET, without any input signal applied, the transistor will conduct. Conversely, with a normally off FET, the transistor may not conduct until an input signal is applied.
Typically, the manufacture of transistors involves several processes. Such processes may include forming a heterostructure using two different semiconductor types, doping a semiconductor to create n and p type regions, and using ion implantation to form the channel of the transistor. These processes add complexity in the manufacturing of a transistor. Furthermore, for some semiconductor types, the creation of a p or n type region may be impracticable.